Powdercoating will not hold up to the heat that an exhaust will put out.
It will end up craking , and looking like crap.
I tried to powdercoat a set of dragpipes for a old bike I had , and was a mess in the long run.
The "Bluing" you are talking about is caused by the heat turning the chrome on the pipe itself. If you are going for this look, get yourself a set of pipes with a very thin layer of chrome , as they will blue nicely. Also , you can take a blowtorch and heat the pipe , and you will get the chrome to turn the bluish tint.
The best coating for an exhaust , in my opinion , is ceramic coating. It is applied very similar to powdercoating , yet it can handle the high temps. All true ceramic coatings are flat in nature , such as flat black , grey , and silver. They can be polished , just like a polished alum. rim , if that is the look you are going after.
I would say go with a flat ceramic coating for your exhaust. It looks great , and is very durable.
That's my 2cents....